The present invention relates to a spread document copying method for a copying machine with a variable modification copying function.
Recently, even a copier with variable magnifications has come to be furnished with a function of copying a document in a spread position. Such a function, which will hereinafter be referred to as a spread document copying function, is accomplished by bisecting a desired face of a book or like spread document into right and left faces and scanning the two faces to reproduce them on copy sheets.
Reference will first be made to FIG. 1 of the drawings for describing the general concept of the spread document copying function. In FIG. 1 and the other drawings, the left and right faces of a spread document will be called faces A and B, respectively. As shown, a spread document (book) 14 is laid on a contact glass 12 with a reference position provided by a document scale 10, while a scanner (not shown) scans the faces A and B of the document 14 to reproduce their images. The images of the faces A and B are sometimes transferred to separate copy sheets and sometimes to opposite surfaces of a single copy sheet.
It will be seen from the above that to copy the face B of a spread document the imaging start position (scanning start position of the scanner) needs be aligned with the end of the face B. Two different methods are available for controlling the imaging start position. One of them is to specify an imaging start position as desired by means of a manually operable lever (with a sensor) and produce images with a document divided into faces A and B. The problem with this approach is that an intricate control mechanism is required resulting in an increase in cost. In addition, the manual operation lacks in efficiency. The other known method is to select an imaging start position depending upon the size of a copy sheet (scanning length). While this second approach successfully solves the problem particular to the first approach, it is incapable of fully copying the face B in the case of magnifications other than a 1 magnification.
The drawback inherent in the second approach mentioned above will be discussed with reference to FIGS. 2-4.
FIG. 2 represents an copying operation with a 1 magnification (magnification M=1). In this condition, the length L of each of the faces A and B of the document 14 is equal to the length l of copy sheets 16 (L=l). The imaging operation starts at a point P.sub.A on the face A and at a point P.sub.B on the face B. The distance l.sub.B from the point P.sub.A to the point P.sub.B is equal to the length L of the surface A or B of the document 14 and the length l of the copy sheets 16 (L=l=l.sub.B), so that both the faces A and B can be fully reproduced on the copy sheets 16. The 1 magnification copying, therefore, is free from the drawback previously described.
FIG. 3 shows a reduction copying operation (magnification M&lt;1) in which case the length L of each face A or B is greater than the length l of copy sheets 16 (L=l/M). For this reason and because the distance l.sub.B between the points P.sub.A and P.sub.B is made equal to the length l of the sheets 16 (l=l.sub.B), a rear end portion 18 of the face A is double-imaged while a rear end portion 20 of the face B is left non-imaged.
FIG. 4 represents an enlargement copying operation (magnification M&lt;1). In this case, the length L of the surfaces A and B of the document 14 is smaller than the length l of the copy sheets 16 and the distance l.sub.B between P.sub.A and P.sub.B is made equal to the length l of the sheets 16 (l=l.sub.B). As a result, a front end portion of the surface B cannot be imaged.
As described above, concerning the system which selects an imaging start position (scan start position in the scanning direction) in conformity to the size of copy sheets, 100% image reproduction cannot be guaranteed unless the magnification M is 1, even though the document size, copy sheet size and magnification may be adequate.